package org.apache.lucene.index;

/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;

/**
 * Abstract class for enumerating terms.
 * 
 * <p>
 * Term enumerations are always ordered by Term.compareTo(). Each term in the
 * enumeration is greater than all that precede it.
 */

public abstract class TermEnum {
	/** Increments the enumeration to the next element. True if one exists. */
	public abstract boolean next() throws IOException;

	/** Returns the current Term in the enumeration. */
	public abstract Term term();

	/** Returns the docFreq of the current Term in the enumeration. */
	public abstract int docFreq();

	/** Closes the enumeration to further activity, freeing resources. */
	public abstract void close() throws IOException;

	// Term Vector support

	/**
	 * Skips terms to the first beyond the current whose value is greater or
	 * equal to <i>target</i>.
	 * <p>
	 * Returns true iff there is such an entry.
	 * <p>
	 * Behaves as if written:
	 * 
	 * <pre>
	 * public boolean skipTo(Term target) {
	 * 	do {
	 * 		if (!next())
	 * 			return false;
	 * 	} while (target &gt; term());
	 * 	return true;
	 * }
	 * </pre>
	 * 
	 * Some implementations are considerably more efficient than that.
	 */
	public boolean skipTo(Term target) throws IOException {
		do {
			if (!next())
				return false;
		} while (target.compareTo(term()) > 0);
		return true;
	}
}
